Steric “attraction”: not by dispersion alone

• Ganna Gryn’ova and
• Clémence Corminboeuf

Beilstein J. Org. Chem. 2018, 14, 1482–1490, doi:10.3762/bjoc.14.125

• Ganna Gryn'ova Clemence Corminboeuf Institut des Sciences et Ingénierie Chimiques, École polytechnique fédérale de Lausanne, CH-1015 Lausanne, Switzerland 10.3762/bjoc.14.125 Abstract Non-covalent interactions between neutral, sterically hindered organic molecules generally involve a strong

• lengths [73]. Conclusion The significance of stabilizing dispersion and electrostatic effects within sterically hindered hydrocarbons is well recognized. In such systems, electrostatic contributions are generally dominated by charge penetration, which increases with system size (bulk) and shorter

Three-component coupling of aryl iodides, allenes, and aldehydes catalyzed by a Co/Cr-hybrid catalyst

• Kimihiro Komeyama,
• Shunsuke Sakiyama,
• Kento Iwashita,
• Itaru Osaka and
• Ken Takaki

Beilstein J. Org. Chem. 2018, 14, 1413–1420, doi:10.3762/bjoc.14.118

• which the cobalt center is connected to a less sterically hindered terminal allene carbon [23]. On the basis of these results, a plausible catalytic cycle for the cobalt/chromium-catalyzed three-component coupling reaction is shown in Scheme 12. The three-component coupling starts with the oxidative

Recent applications of chiral calixarenes in asymmetric catalysis

• Mustafa Durmaz,
• Erkan Halay and
• Selahattin Bozkurt

Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117

• in the presence of NaH or n-BuLi (Figure 5) [46]. Conformational analysis of calixarene-diphosphite ligands revealed that presence of sterically hindered groups led to the formation of the predominantly cone-conformer. In order to check whether calix[4]arene-diphosphite ligands may also serve as

A three-armed cryptand with triazine and pyridine units: synthesis, structure and complexation with polycyclic aromatic compounds

• Claudia Lar,
• Adrian Woiczechowski-Pop,
• Attila Bende,
• Ioana Georgeta Grosu,
• Natalia Miklášová,
• Elena Bogdan,
• Niculina Daniela Hădade,
• Anamaria Terec and
• Ion Grosu

Beilstein J. Org. Chem. 2018, 14, 1370–1377, doi:10.3762/bjoc.14.115

• design of the cryptand by replacing the central benzene ring with a triazine unit (in which the H atoms of the ortho positions are replaced by lone electron pairs belonging to the N atoms). The resulting less sterically hindered cryptand 2 (Figure 1) was then tested for its ability to form host–guest

Synthesis of chiral 3-substituted 3-amino-2-oxindoles through enantioselective catalytic nucleophilic additions to isatin imines

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 1349–1369, doi:10.3762/bjoc.14.114

•  20. In 2016, Zhang and Yang reported an asymmetric palladium-catalyzed addition of arylboronic acids 60 to sterically hindered N-tert-butylsulfonylisatin imines 61 [80]. Among a variety of chiral ligands investigated, including different pyridine-oxazolines, oxazolines and (R)-BINAP, the chiral

A survey of chiral hypervalent iodine reagents in asymmetric synthesis

• Soumen Ghosh,
• Suman Pradhan and
• Indranil Chatterjee

Beilstein J. Org. Chem. 2018, 14, 1244–1262, doi:10.3762/bjoc.14.107

• plausible mechanism and transition-state model 27 for the formation of the major isomer through the attack of the carboxylic acid group to the ipso position of the naphthol ring from the less sterically hindered Re-face of the substrate 25. It is worth mentioning that very recently they have introduced a

• postulated the formation of possible intermediate 97 which favored the nucleophilic attack of the aryl ring from the less sterically hindered side. Later, Du et al. used this same precatalyst 12 to obtain spirofurooxindole derivatives with high enantioselectivity through cascade cross-coupling sequences [71

• , nucleophilic fluorinating technique of β-keto esters 102 using 106/HF/m-CPBA as a catalytic system to access fluorinated β-keto esters 103 with moderate enantioselectivity [73]. β-Keto esters having sterically hindered adamantyl or menthyl groups lead to good selectivity. However, no further enhancement of ee

Recyclable hypervalent-iodine-mediated solid-phase peptide synthesis and cyclic peptide synthesis

• Dan Liu,
• Ya-Li Guo,
• Jin Qu and
• Chi Zhang

Beilstein J. Org. Chem. 2018, 14, 1112–1119, doi:10.3762/bjoc.14.97

• obtain various dipeptides from standard amino acids as well as sterically hindered amino acids. Moreover, a pentapeptide Leu-enkephalin is successfully synthesized in its protected form using this coupling system. Similar to iodosodilactone, FPID can be easily regenerated after the reaction. The

Cross-coupling of dissimilar ketone enolates via enolonium species to afford non-symmetrical 1,4-diketones

• Keshaba N. Parida,
• Gulab K. Pathe,
• Shimon Maksymenko and
• Alex M. Szpilman

Beilstein J. Org. Chem. 2018, 14, 992–997, doi:10.3762/bjoc.14.84

• avoided simply by using the reverse addition to give the desired product 13 in good yield. The choice of the order of addition is also of importance for substrates with more sterical hindrance. Here the trend is clear: it is advantageous to use the less sterically hindered TMS enol ether to generate the

• enolonium species 4 followed by the addition of the more sterically hindered TMS enol ether 5. For example, the addition of enolonium species 4 (R1 = Ph, R2 = Me) to the TMS enol ether 5 (R3 = Ph, R4 = H) led to formation of the product 14 in 30% yield with significant formation of 1-tosyloxypropiophenone

• as the major byproduct. However, when the order of addition was reversed, i.e., the enolonium species 4 (R1 = Ph, R2 = H) was cross-coupled with TMS enol ether 5 (R3 = Ph, R4 = Me) the same product 14 was obtained in 74% yield. Apparently, in these cases the sterically hindered nature of the

Nanoreactors for green catalysis

• M. Teresa De Martino,
• Loai K. E. A. Abdelmohsen,
• Floris P. J. T. Rutjes and
• Jan C. M. van Hest

Beilstein J. Org. Chem. 2018, 14, 716–733, doi:10.3762/bjoc.14.61

• these Pd-catalytic micelles was also achieved while catalyzing reactions involving less reactive or sterically hindered species. Handa et al. described a self-assembled TPGS-750M micelle (shown in Scheme 1), that allowed for copper-catalyzed Suzuki–Myaura coupling of aryl iodides (Scheme 2) [70]. When

Enhanced quantum yields by sterically demanding aryl-substituted β-diketonate ancillary ligands

• Rebecca Pittkowski and
• Thomas Strassner

Beilstein J. Org. Chem. 2018, 14, 664–671, doi:10.3762/bjoc.14.54

• properties can be tuned by variation of the ligands or by specific electron-withdrawing or electron-donating substituents. Different ancillary ligands can have a profound impact on the emission color and emission efficiency of these complexes. We studied the influence of sterically hindered, aryl-substituted

Oxidative cycloaddition of hydroxamic acids with dienes or guaiacols mediated by iodine(III) reagents

• Hisato Shimizu,
• Akira Yoshimura,
• Keiichi Noguchi,
• Victor N. Nemykin,
• Viktor V. Zhdankin and
• Akio Saito

Beilstein J. Org. Chem. 2018, 14, 531–536, doi:10.3762/bjoc.14.39

• regioselectivities observed for 3ae, 3be [12][36], and 6 [34] are in consistency with experimental data as well as the results of FMO and DFT calculations. The decline in regioselectivity of 3ce may be due to steric repulsion between the sterically hindered tert-butyloxycarbonyl group in 1c with the 2-methyl

Palladium-catalyzed ortho-halogenations of acetanilides with N-halosuccinimides via direct sp² C–H bond activation in ball mills

• Zi Liu,
• Hui Xu and
• Guan-Wu Wang

Beilstein J. Org. Chem. 2018, 14, 430–435, doi:10.3762/bjoc.14.31

• acetanilides were obtained in moderate to good isolated yields. Both p-Me and m-Me-substituted acetanilides provided products 2a and 2b in excellent yields of 87% and 80%, respectively (Table 2, entries 1 and 2). As expected, 3,4-dimethylacetanilide underwent iodination successfully at the less sterically

• hindered ortho-position and gave product 2c in 85% yield (Table 2, entry 3). The unsubstituted acetanilide provided the desired product 2d in 77% yield (Table 2, entry 4). It is worth mentioning that the presence of a potentially reactive group, such as fluoro, chloro, and bromo substituents in the

Recent developments in the asymmetric Reformatsky-type reaction

• Hélène Pellissier

Beilstein J. Org. Chem. 2018, 14, 325–344, doi:10.3762/bjoc.14.21

• that of sulfinyl imines (S)-25c,d exhibiting an α-benzyloxy substituent provided high diastereoselectivities (76–88% de). This assumed the coordination of the α-alkoxy group to zinc. Even a higher diastereoselectivity of >90% de was achieved for more sterically hindered α-alkoxy-derived substrates (S

• (79–93% ee). Notably, even sterically hindered cyclic imines bearing two substituents were compatible, providing the corresponding products in high enantioselectivities (79–93% ee). Moreover, the use of ketimines in such reactions represented a challenge, owing to their low reactivity and steric

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

• Ranjana Aggarwal and
• Suresh Kumar

Beilstein J. Org. Chem. 2018, 14, 203–242, doi:10.3762/bjoc.14.15

• formed by addition from the less sterically hindered amino group. The free amino group was alkylated by reductive amination on reaction with substituted aldehyde or ketones to provide the corresponding pyrazolo[1,5-a]pyrimidine derivatives 139 (Scheme 39). The pyrazolo[1,5-a]pyrimidine derivatives 139

Progress in copper-catalyzed trifluoromethylation

• Guan-bao Li,
• Chao Zhang,
• Chun Song and
• Yu-dao Ma

Beilstein J. Org. Chem. 2018, 14, 155–181, doi:10.3762/bjoc.14.11

• required for the conversion of electron-deficient derivatives. Besides, sterically hindered boronic acids were also tolerated in this reaction. This protocol was simplified and easy-to-handle and no protodeboronation byproduct was observed under these conditions, while the major side product (the

Aminomethylation/hydrogenolysis as an alternative to direct methylation of metalated isoquinolines – a novel total synthesis of the alkaloid 7-hydroxy-6-methoxy-1-methylisoquinoline

• Benedikt C. Melzer,
• Jan G. Felber and
• Franz Bracher

Beilstein J. Org. Chem. 2018, 14, 130–134, doi:10.3762/bjoc.14.8

• metalations of isoquinolines at C1 with sterically hindered amide bases like TMPMgCl∙LiCl (Knochel–Hauser base) [6]. For our present purpose, an appropriate 1-metalated isoquinoline species was to be converted into the corresponding 1-methyl product. Since the 7-hydroxy group of target alkaloid 1 is not

Fluorescent nucleobase analogues for base–base FRET in nucleic acids: synthesis, photophysics and applications

• Mattias Bood,
• Sangamesh Sarangamath,
• Moa S. Wranne,
• Morten Grøtli and
• L. Marcus Wilhelmsson

Beilstein J. Org. Chem. 2018, 14, 114–129, doi:10.3762/bjoc.14.7

• -iodoaniline 32 in 68% yield after isolation [52]. The cyclization was performed via nucleophilic aromatic substitution with DBU and DABCO. Presumably DABCO activates the chlorine and modifies it into a better leaving group allowing the sterically hindered base DBU to abstract a proton from the protected

Synthesis and supramolecular properties of regioisomers of mononaphthylallyl derivatives of γ-cyclodextrin

• Markéta Bláhová,
• Sergey K. Filippov,
• Lubomír Kováčik,
• Jiří Horský,
• Simona Hybelbauerová,
• Zdenka Syrová,
• Tomáš Křížek and
• Jindřich Jindřich

Beilstein J. Org. Chem. 2017, 13, 2509–2520, doi:10.3762/bjoc.13.248

• group at position 2 is the most acidic, and the group at position 3 is most sterically hindered. Therefore, regioselective monosubstitution to positions 2 and 6 can be controlled by the amount and strength of the base used in the reaction, whereas monosubstitution at position 3 can be achieved by

Electron-deficient pyridinium salts/thiourea cooperative catalyzed O-glycosylation via activation of O-glycosyl trichloroacetimidate donors

• Mukta Shaw,
• Yogesh Kumar,
• Rima Thakur and
• Amit Kumar

Beilstein J. Org. Chem. 2017, 13, 2385–2395, doi:10.3762/bjoc.13.236

• system on glycosylation of 1α with several acceptors (Table 2). In all cases, reactions proceeded smoothly within 2–6 h and in good yields with moderate to good selectivity, as determined by the 1H and 13C NMR spectra. Glycosylation with less sterically hindered primary alcohols, e.g., allyl alcohol (2b

One-pot syntheses of blue-luminescent 4-aryl-1H-benzo[f]isoindole-1,3(2H)-diones by T3P^® activation of 3-arylpropiolic acids

• Melanie Denißen,
• Alexander Kraus,
• Guido J. Reiss and
• Thomas J. J. Müller

Beilstein J. Org. Chem. 2017, 13, 2340–2351, doi:10.3762/bjoc.13.231

• consecutive transformations. For instance, para-substituted halogenated anilines 3 (Table 5, entries 3–5) and ethyl 4-aminobenzoate (Table 5, entry 6) furnish the desired products in 51–65% yield. Interestingly, also sterically hindered anilines, such as 2,6-dimethylaniline can be obtained in 56% yield (Table

Dialkyl dicyanofumarates and dicyanomaleates as versatile building blocks for synthetic organic chemistry and mechanistic studies

• Grzegorz Mlostoń and
• Heinz Heimgartner

Beilstein J. Org. Chem. 2017, 13, 2235–2251, doi:10.3762/bjoc.13.221

• type 19 and cyclopropanes of type 15 in which Me2C is replaced by H2C was observed when the sterically hindered S-methanide derived from 2,2,6,6-tetramethylcyclohexanethione was reacted with E- or Z-1b [26], whereas in the cases of 2,2,5,5-tetramethylcyclopentanethione and 1,1,3,3-tetramethylindane-2

Conjugated nitrosoalkenes as Michael acceptors in carbon–carbon bond forming reactions: a review and perspective

• Yaroslav D. Boyko,
• Valentin S. Dorokhov,
• Alexey Yu. Sukhorukov and
• Sema L. Ioffe

Beilstein J. Org. Chem. 2017, 13, 2214–2234, doi:10.3762/bjoc.13.220

• ). It is believed that the initially formed α-cyanooximes 85 undergo rapid cyclization to isoxazole derivatives 86. Interestingly, in the case of a more sterically hindered 3-chloronorcamphor oxime, the corresponding α-cyanooxime 85a was obtained, which did not undergo cyclization to isoxazole

Phosphonic acid: preparation and applications

• Charlotte M. Sevrain,
• Mathieu Berchel,
• Hélène Couthon and
• Paul-Alain Jaffrès

Beilstein J. Org. Chem. 2017, 13, 2186–2213, doi:10.3762/bjoc.13.219

• acidification with hydrochloric acid. For example, the sterically hindered phenylphosphonic acid 85 was prepared in a two-step procedure starting from the dichlorophenylphosphine 83. Ph–PCl2 was first oxidized into the phenylphosphine oxide 84 with sulfuryl chloride in CCl4 and then hydrolysis occurred with

Preactivation-based chemoselective glycosylations: A powerful strategy for oligosaccharide assembly

• Weizhun Yang,
• Bo Yang,
• Sherif Ramadan and
• Xuefei Huang

Beilstein J. Org. Chem. 2017, 13, 2094–2114, doi:10.3762/bjoc.13.207

• utilized glycosyl sulfoxide donors for glycosylation of unreactive substrates such as steroid derivative 2 by the Kahne group [25]. The axial C-7 hydroxy group in 2 is sterically hindered due to unfavorable 1,3-diaxial interactions. The traditional premixed glycosylation gave only low yields (<30%) of the

Mechanochemical synthesis of thioureas, ureas and guanidines

• Vjekoslav Štrukil

Beilstein J. Org. Chem. 2017, 13, 1828–1849, doi:10.3762/bjoc.13.178

• -type amine–isothiocyanate coupling reaction (Scheme 4). In the case of secondary amines (piperidine, morpholine and thiomorpholine) and sterically hindered amines (2,4- and 2,6-dimethylanilines), ball milling again resulted in ≥99% yields in 10 minutes, except for the reactions involving 4

• : corrugated chains of head-to-head or head-to-tail aligned molecules and discrete centrosymmetric dimers based on the R22(8) supramolecular synthon in the case of sterically hindered thioureas (Figure 2). The crystal structures of N,N'-diarylthioureas linked in chains via N–H···S hydrogen bonds can further be

• bis-thioureas which were tested as cyanide anion sensors in DMSO solution. Our group continued the research on the solid-state synthesis of thioureas focusing now on the reactivity of sterically hindered ortho-phenylenediamine (o-pda) with isothiocyanates [35]. Whereas Kaupp's approach to prepare a